Berlin 2024 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 46: Transport properties II

HL 46.4: Talk

Thursday, March 21, 2024, 15:45–16:00, ER 325

Counter-Ion Size Effect on the Thermoelectric Properties of Doped Carbon Nanotubes Network — •Aditya Dash¹, Angus Hawkey², Dorothea Scheunemann¹, Jana Zaumseil², and Martijn Kemerink¹ — ¹Institute for Molecular Systems Engineering and Advanced Materials, Heidelberg University, Im Neuenheimer Feld 225, 69120 Heidelberg, Germany — ²Institute for Physical Chemistry, Universität Heidelberg, D-69120 Heidelberg, Germany

Doping is a proven technique to improve the thermoelectric properties of semiconducting single-walled carbon nanotube networks, which are promising for the conversion of waste heat to electricity. For this, understanding the counter-ion size effect is crucial, as Coulombic interactions between the ions and the free charge carriers cause scattering and trapping. Here, we propose a random resistor network model that accounts for the formation of Coulombic traps at low doping levels, and the formation of an impurity band at high doping levels. As such, it accounts for the increasing overlap of the Coulombic potentials due to dopant ions. The model semi-quantitatively reproduces our experiments that demonstrate that larger counter-ions enhance conductivity and maximize the power factor before a saturation sets in. Moreover, the conductivity dependence on ionic size is stronger at low temperatures. Overall, the employed model may guide the counter-ion selection to improve thermoelectric efficiency, depending on the interplay between the achievable doping level, ion size and the energetic disorder in the network.

Keywords: Thermoelectrics; Carbon Nanotubes; Doping; Counter-ion size; Disorder